xdrgen: Fix return code checking in built-in XDR decoders

xdr_stream_encode_u32() returns XDR_UNIT on success.
xdr_stream_decode_u32() returns zero or -EMSGSIZE, but never
XDR_UNIT.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/xdrgen/_builtins.h

@@ -184,7 +184,7 @@ xdrgen_decode_string(struct xdr_stream *xdr, string *ptr, u32 maxlen)
 	__be32 *p;
 	u32 len;
 
-	if (unlikely(xdr_stream_decode_u32(xdr, &len) != XDR_UNIT))
+	if (unlikely(xdr_stream_decode_u32(xdr, &len) < 0))
 		return false;
 	if (unlikely(maxlen && len > maxlen))
 		return false;
@@ -215,7 +215,7 @@ xdrgen_decode_opaque(struct xdr_stream *xdr, opaque *ptr, u32 maxlen)
 	__be32 *p;
 	u32 len;
 
-	if (unlikely(xdr_stream_decode_u32(xdr, &len) != XDR_UNIT))
+	if (unlikely(xdr_stream_decode_u32(xdr, &len) < 0))
 		return false;
 	if (unlikely(maxlen && len > maxlen))
 		return false;

tools/net/sunrpc/xdrgen/templates/C/pointer/decoder/variable_length_array.j2

@@ -2,7 +2,7 @@
 {% if annotate %}
 	/* member {{ name }} (variable-length array) */
 {% endif %}
-	if (xdr_stream_decode_u32(xdr, &ptr->{{ name }}.count) != XDR_UNIT)
+	if (xdr_stream_decode_u32(xdr, &ptr->{{ name }}.count) < 0)
 		return false;
 {% if maxsize != "0" %}
 	if (ptr->{{ name }}.count > {{ maxsize }})

tools/net/sunrpc/xdrgen/templates/C/struct/decoder/variable_length_array.j2

@@ -2,7 +2,7 @@
 {% if annotate %}
 	/* member {{ name }} (variable-length array) */
 {% endif %}
-	if (xdr_stream_decode_u32(xdr, &ptr->{{ name }}.count) != XDR_UNIT)
+	if (xdr_stream_decode_u32(xdr, &ptr->{{ name }}.count) < 0)
 		return false;
 {% if maxsize != "0" %}
 	if (ptr->{{ name }}.count > {{ maxsize }})

tools/net/sunrpc/xdrgen/templates/C/union/decoder/variable_length_array.j2

@@ -2,7 +2,7 @@
 {% if annotate %}
 		/* member {{ name }} (variable-length array) */
 {% endif %}
-		if (xdr_stream_decode_u32(xdr, &count) != XDR_UNIT)
+		if (xdr_stream_decode_u32(xdr, &count) < 0)
 			return false;
 		if (count > {{ maxsize }})
 			return false;